The present invention relates to a device for the leaktight attachment of semi-permeable membranes to support plates of an apparatus which separates by selective permeability.
Apparatuses which separate fluid by selective permeability are known, especially from French Pat. No. 2,127,155 and its Certificate of Addition No. 2,141,417. These apparatuses comprise sub-units which are formed, in particular, by the juxtaposition of a number of membrane support plates, the pressurized fluid to be treated, which is generally liquid, circulating in parallel between the membranes of the successive support plates (of one sub-unit), which are provided with, generally elongated, orifices towards each of their ends, for the passage of the fluid, while this fluid circulates in series from one sub-unit to the other due to the presence of so-called intermediate plates which only have an orifice towards one of their ends. When it has passed through the membranes, the fluid is recovered individually for each support plate on the edge of the latter.
French Pat. No. 2,165,042 has proposed a solution for keeping the membranes leaktight near the orifices, for the passage of the fluid to be treated, of each support plate. This solution consists in keeping the transverse ends of the membrane in an elongated opening, which is close to the orifice for the passage of the fluid to be treated, by means of a detachable device which keeps the membrane leaktight on the inner wall of this opening. It has been shown that, under certain conditions of use of the apparatus, and especially for high circulation rates of the fluid to be treated, this detachable device can advantageously be replaced by a device, which is preferably of circular shape, the fluid to be treated circulating at the center thereof. Such a device for the leakproof attachment of membranes to a support plate is already known, but it exhibits the disadvantage that it is not itself fixed to a support plate, which requires that the adjacent devices of two consecutive support plates be held in contact with one another, for example, by means of cams or peripheral ridges, in which case the membranes are only kept leaktight on the support plates when the apparatus is tightened up. This embodiment of the membrane fixing device, therefore, only makes it possible to ensure the leaktight attachment of the membranes to each opposite face and around the orifice, for the passage of the fluid to be treated, of a support plate when the apparatus itself is tightened up. This embodiment of the attaching devices, therefore, exhibits the disadvantage that it renders the leaktightness of the membranes on each support plate dependent on the tightening-up of the apparatus itself, which tightening-up must also make it possible to ensure the peripheral leaktightness between two consecutive membrane support plates.